1. Field of the Invention
The invention pertains to radar target detection in a clutter environment and more particularly to the removal of clutter correlation introduced by a video enhancer in the video processing stage.
2. Description of the Prior Art
An important problem in the automatic detection and tracking of targets in air surveillance radars is the variation of false alarm rates with changing noise and clutter conditions. This problem has been the motivating force in the development of a multiplicity of constant false alarm rate (CFAR) receivers. One approach to CFAR processing is to use nonparametric techniques, such as the rank quantizer, wherein the signal level at the center tap of a tapped delay line is compared to the signal level at all other taps along the line, the rank of the central tap being the number of comparisons for which the signal amplitude at the tap is the greater of the two signal amplitudes. The rank obtained for the central tap after each transmitted pulse is then compared to a predetermined threshold and the number of ranks exceeding this threshold are summed after a number of transmitted pulses. The sum so obtained is then compared to a second threshold to determine a signal detection. Rank quantizers with post detection integration possess, CFAR characteristics, independent of noise and clutter distribution, for azimuthally uncorrellated noise and clutter.
Many air traffic surveillance site radars are commonly operated in the enhanced video mode. In this mode the radar video is fed through a video enhancer, prior to coupling the video to the display, that improves the target video while reducing the noise level. This process, however, adversely effects the CFAR characteristics by introducing significant azimuth clutter correllation, which may increase the false alarm rate to unacceptable levels. It is therefore desirable to provide a circuit to remove the azimuth clutter correllation introduced by the video enhancer.